The invention relates to a method and arrangement for cleaning filters through which raw gas with particles suspended therein flows from a raw gas space to a clean gas space, whereby the particles are collected on the filter and through which, from time to time, a back-flushing gas is conducted from the clean gas space to the raw gas space while any outlet from the clean gas is blocked to dislodge and carry away particles collected on the filter.
The invention is particularly concerned with the cleaning of compact filters while they remain installed in a filter housing. Cleaning units, which also operate according to the same principle, generally include a movable member, which is moved in the clean gas space over the filter elements and partially or fully seals off the filter elements. This member is operated, directly or indirectly, generally by mechanical and pneumatic drive units. Another arrangement for cleaning a filter comprises round or slot-like nozzle systems at the clean gas side of the filter element. Such devices are known in connection with hose and pocket-type filters.
Such mechanical cleaning arrangements are subject to failure and involve relatively high design and construction expenses. Critical is the seal toward the filter elements, which is achieved by way of a flexible seal that is subjected to high wear. With the guiding of the movable member at the same time a high sealing force has to be applied which increases the wear of the seal. With regard to the large number of cleaning cycles, the whole design must be made to be very sturdy. As a result, the structure is relatively heavy so that high drive forces are required, the design is relatively expensive and the cleaning of large filter elements is complicated. It has therefore been tried to clean several filter elements at the same time, whereby however, the back-flushing air volume available per filter element is reduced. With the use of movable parts for driving the member, the acceptable gas temperature is substantially lower than the temperature, which the filter element can withstand.
The embodiment which uses rigidly mounted nozzles involve unacceptably high expenses for large filter systems particularly with pleated filters having deep pleats and 50 or more pleats in each filter element. Since there is no direct coupling of the cleaning unit with the filter, only low cleaning intensities can be generated.
DE-U-9000579 discloses a filter apparatus with split filter cartridges, wherein the split filter cartridges can be cleaned from the clean gas side by means of a back-flushing gas flow. In that arrangement for each split filter cartridge, there is provided a check valve in the form of a closing flap, that is, a moving part which, at a predetermined pressure, blocks the gas flow from the filter cartridge. For cleaning the filter cartridges, the back-flushing gas is introduced into the clean gas space between the split filter cartridge and the check valve, whereby the check valve is closed by the increased gas pressure, and the split filter cartridge is cleaned by a counter-current gas flow through the filter into the raw gas space.
Further, EP 0 551 951 B1 discloses a method for cleaning filters, through which a raw gas is conducted from one side, by back-flushing of the filters from the clean gas side. The flushing gas stream required for the back-flushing is conducted through chambers disposed between the filters and a second filter surface. This second filter surface has a permeability, which is greater than that of the filter to be cleaned by a factor of 3-5 and a larger pore size and a filter surface area, which is smaller than that of the filter to be cleaned by a factor of up to 10. In this arrangement, which has no moving parts, the back-flushing gas flow is conducted through this second filter area and is therefore limited.
It is the object of the present invention to provide a method and arrangement for cleaning cartridge-type aerosol filters in an efficient and effective manner without the use of movable components, which are subject to failure.
In a method and apparatus for cleaning filters in which raw gas with particles suspended therein conducted from a raw gas space to a clean gas space and through which intermittently a back-flushing gas is conducted from the clean gas space to the raw gas space, a flow dynamic control element is disposed in the clean gas space which blocks the outflow of gas from the clean gas space when a back-flushing gas is admitted to the clean gas space under a pressure, which exceeds the filter operating pressure so as to prevent excessive back-flushing gas losses during back-flushing. The flow dynamic control element is switched between an open and a blocking state by the pressure changes in the clean gas space without including any movable parts.
The invention therefore provides for a method and arrangement with which the filters can be cleaned efficiently and effectively in a simple manner without the use of moving parts. Larger filter units can therefore be very compact in design and economical to construct which is highly advantageous for the use of back-flushable aerosol filters for example in power generation plants.
Particulars of the invention will become more readily apparent from the following description on the basis of the accompanying drawings.